DE 10 2013 02 046 B3 discloses a combustion chamber assembly unit for a fuel-operated vehicle heater, in which a flange-like support area extending radially outwards from a combustion chamber housing is held between a first outer housing and a second outer housing. In this connection, the first outer housing is, for example, associated with a combustion air guide blower, while the second outer housing may be associated, for example, with a heat exchanger arrangement. In order to be able to obtain a fluid-tight connection of the flange-like support area in relation to the first outer housing and in relation to the second outer housing, a sealing element with a U-shaped cross section made of flexible material, e.g., silicone, extending entirely around the radial outer area of the support area, is provided. This flexible sealing element with U-shaped cross section can be pulled from the outside over the entire circumferential area of the support area because of its elasticity and its stretchability, such that in the assembled state, it extends continuously over the entire circumferential area, enclosing the support area radially outwards and overlapping radially inwards on both axial sides in some sections.